This invention relates to an apparatus and method for detecting the position of an article such as, for example, an optical waveguide fiber. More particularly, this invention relates to a simplified and compact apparatus for optically determining the X and Y positions of a fiber coupled with a circuit for providing output signals indicative of such X and Y positions. The output signals may be employed to control a feedback operation such as the positioning of the fiber relative to a coater.
Glass optical waveguide fibers must exhibit high strength in order to withstand the stresses which are encountered during incorporation into protective sheathing or cable, installing the cable, or during use thereof. While such fibers are typically quite strong as drawn from a preform, crucible, or the like, this strength is rapidly degraded by surface defects which are introduced into the fiber through handling or otherwise.
To preserve the strength of a newly drawn fiber it is conventional to apply to the fiber, immediately after it is drawn, a thin protective coating composed of an organic or inorganic coating material which serves to protect the fiber during subsequent handling. Typical fiber coating apparatus is disclosed in U.S. Pat. Nos. 4,194,462 and 4,264,649. Both of these patents teach the use of an X-Y positioner to position the coater with respect to the fiber so that the fiber is substantially centered in the coating die. Such positioning prevents the uncoated fiber from being damaged by contacting the coating apparatus and ensures the application of substantially concentric coatings. Various means have been employed to determine the position of a fiber within the coating apparatus. The aforementioned U.S. Pat. No. 4,264,649 teaches the use of a television camera which is directed toward the output orifice of the coating apparatus so that the position of the fiber therein can be observed on a monitor. Another method for determining fiber position employs two sources of collimated light directed orthogonally onto the fiber. The light beams from the two sources are then directed onto two detectors, which may comprise scanned diode arrays. The outputs from the arrays may be connected to electronic circuits which drive digital displays that read out the X and Y positions of the fiber. An operator can observe the position of the fiber by reading the displays and can then manually adjust either the coater position or the fiber source to center the fiber in the coating apparatus. Alternatively, the outputs from the scanned diode arrays may be connected to X and Y positioning motors which automatically perform such fiber centering functions.